Slide 55 of 66
Notes:
The final topic to be addressed with regard to transient landform evolution is the dissection of regolith-covered landscapes by gullying, as shown in this picture of a gully progressing headwards along a hollow on a slope in the Coast Ranges of California. The simulations shown here are presented in Howard (1999, op. Cit.). Gullying is a serious problem in some landscapes where deep, erodible regolith (or weak, shale bedrock) occurs beneath a normally coherent vegetation layer. The thesis of the simulations is that a coherent vegetation cover is a strong deterrent to erosion, and its resistance to erosion is nearly as great as that of unweathered bedrock. When the vegetation is disturbed, as a result of fire, disease, climatic change, human interference, incision of the master stream, or even severe storms, a cycle of incision can result in which a gully incises below the vegetation level, and then progresses to consume much of the landscape by headward erosion and undermining of the vegetation, replacing the normally rolling upland by steep badland slopes along the gully walls.
